Hydraulic Cylinder Force, Speed & Repair Worksheet

What the calculation means

With bore D and rod d in mm, piston area A = πD²/4 and annular area B = π(D² − d²)/4. Inlet pressure p and return pressure r are in bar. Extension force is (pA − rB)/10,000 kN; retraction force is (pB − rA)/10,000 kN. Inlet flow Q in L/min gives speed Q × 1,000,000/(60 × active area) mm/s. Stroke time is stroke divided by speed. Return flow is inlet flow multiplied by opposite area / active area.

Each column assumes the same entered inlet pressure, return pressure and inlet flow applied separately in that direction. It is not a simultaneous circuit simulation. Results ignore friction, leakage, acceleration, fluid compressibility, line losses and cushioning. They do not rate a load, mounting, rod against buckling or the machine for service. Regenerative, telescopic, differential and double-rod circuits need a different model.

Worked example: why extension and retraction differ

Illustrative numbers, not a field case: 80 mm bore, 45 mm rod, 500 mm stroke, 160 bar inlet, 5 bar return and 20 L/min inlet. The effective areas are 5,026.55 and 3,436.12 mm². Ideal net force is 78.71 kN extending and 52.46 kN retracting. Ideal stroke times are 7.54 and 5.15 seconds. On retraction the calculated return flow is 29.26 L/min, greater than the 20 L/min inlet flow. That difference is a reason to check circuit data, not to fit a larger pump.

Use the comparison without jumping to a seal order

1. Confirm the inputs. A pump nameplate value is not proof that the same flow reaches the cylinder under load. Mark assumptions in your notes.
2. Compare like with like. Use records for the same stroke, load, direction and oil condition. A shorter timed stroke cannot be compared directly with a full-stroke estimate.
3. Separate force and speed. Slow travel can come from available flow, a restriction or leakage. Weak force can involve pressure, load or mechanical geometry. Neither result proves piston-seal bypass.
4. Keep the evidence. Print the input values, result and observations. Ask the repairer which measurement or manufacturer procedure would distinguish the remaining causes.